Hydrothermal synthesis and characterization of nitrogen-doped fluorescent carbon quantum dots from citric acid and urea

As a new type of fluorescent carbon nanomaterials, carbon quantum dots have been widely concerned in recent years because of their good biocompatibility, low cytotoxicity and easy surface functionalization. In this paper, nitrogen-doped carbon quantum dots (N-CQDs) were prepared by one-step hydrothermal method with citric acid as the carbon source and urea as a nitrogen source. The fluorescence spectrophotometer, Fourier infrared spectrometer, X-ray diffractometer, and transmission electron microscope were utilized to discover the luminescence properties, structural characteristics, morphology and size of the synthesized N-CQDs. The results showed that the best reaction conditions for preparing N-CQDs were as follows: the hydrothermal process parameters were 240 °C for 10 h, and the concentration of nitrogen doping was 0.6 wt%. Under these conditions, the prepared N-CQDs with bright blue fluorescence solution was uniform and stable. And the results showed the structural characteristics were weak crystalline graphite carbon, and the shape characteristics were nearly spherical quantum dot with about 5–10 nm diameters.